A cenote is a natural pit or sinkhole that forms when limestone bedrock collapses, revealing a pool of groundwater below. The term originates from the Yucatec Maya word “ts’ono’ot,” which refers to any location with accessible groundwater. These unique geological formations are windows into vast subterranean water systems.
Geological Formation
Cenotes primarily form through a geological process known as karstification, involving the dissolution of soluble bedrock. The Yucatán Peninsula, largely composed of porous limestone, provides an ideal environment for this process. Rainwater, which becomes slightly acidic after absorbing carbon dioxide from the atmosphere and soil, seeps into the ground. Over millions of years, this acidic water slowly dissolves the limestone, creating intricate underground voids, passages, and extensive cave systems.
As these underground cavities enlarge, the overlying rock can lose its structural integrity. Eventually, the ceiling of these caverns may collapse, exposing the groundwater and forming a cenote. The Chicxulub meteorite impact approximately 66 million years ago also influenced cenote formation in the Yucatán, by creating fractures in the bedrock that allowed water to penetrate more easily.
Distinct Characteristics and Global Presence
Cenotes exhibit a variety of appearances and features. Cave cenotes, considered the youngest, are enclosed underground caverns accessible through small openings, often adorned with stalactites and stalagmites. Semi-open cenotes represent a middle stage, where parts of the cave roof have collapsed, allowing sunlight to filter into the water below.
Open cenotes are the oldest type, characterized by a completely collapsed roof, resembling natural, open-air pools or lakes. Some ancient cenotes show further transformation, with water levels receding and exposing steep, cliff-like walls. While the Yucatán Peninsula in Mexico has an estimated 6,000 to 10,000 cenotes, these formations also exist in other regions worldwide. Similar karst features can be found in places like Cuba, Australia, the United States, Canada, Belize, and the Dominican Republic.
Ecological and Cultural Significance
Cenotes are unique freshwater ecosystems, supporting distinct flora and fauna. Their clear waters, filtered through the ground, provide habitats for various aquatic species, including guppies, catfish, and endemic blind cave fish and blind swamp eels. Land-dwelling creatures like turtles, iguanas, frogs, and bats also frequent the areas around cenotes, alongside birds such as swallows that nest on their walls.
The Maya regarded cenotes as culturally and spiritually significant, serving as the primary source of fresh water in the Yucatán Peninsula where surface rivers are scarce, enabling major Maya settlements to thrive. They were regarded as sacred wells and portals to Xibalba, the underworld. Rituals and offerings were performed in cenotes to communicate with deities like Chaac, the rain god.